Lecture 4 - Engineering project Scheduling.pptx

Construction project Scheduling

1. Scheduling M Bilal Zahid

2. Scheduling Real-life projects involve hundreds of activities, it is important to identify the group of critical activities so that special care is taken to make sure they are not delayed. All these statements are the basic objectives of the scheduling process , which adds a time dimension to the planning process. In other words, we can briefly state that: Scheduling = Planning + Time. 2

3. Key Questions How can the project be displayed graphically to better visualize the flow of the activities? What is the total time required to complete the project if no delays occur? When do the individual activities need to start and finish (at the latest) to meet this project completion time? When can the individual activities start and finish (at the earliest) if no delays occur? Which are the critical bottleneck activities where any delays must be avoided to prevent delaying project completion? For the other activities, how much delay can be tolerated without delaying project completion? Given the uncertainties in accurately estimating activity durations, what is the probability of completing the project by the deadline? If extra money is spent to expedite the project, what is the least expensive way of attempting to meet the target completion time (40 weeks)? How should ongoing costs be monitored to try to keep the project within budget? 3

4. Key Questions CPM (critical path method) and PERT (program evaluation and review technique) are available to assist the project manager in answering these questions. 4

5. Activity Durations 5

6. Activity Durations Each activity has an associated time duration. Durations are used in preparing a schedule. Historical records of particular activities and rely on the average durations from this experience in making new duration estimates. One effective way of estimating an activity duration is to compute it by applying a crew or equipment production rate to the total number of units of work to be done. 6

7. Activity Durations The duration of an activity may be estimated as: Quantity of work is determined from engineering drawings Number of crews working is decided by the planner Amount of resources applied to particular activities may be modified in light of the resulting project plan and schedule Some estimate of the expected work productivity must be provided Knowing activity duration and resources employed, it is simple to estimate the activity direct cost.   7

8. Activity Durations Example: If the daily production rate for a crew that works in an activity is 175 units/day and the total crew cost per day is 1800 PKR. The material needed for daily work is 4.5 units at 1000 PKR/unit. Calculate the time and cost it takes the crew to finish 1400 units. Calculate the total unit cost. Consider an eight hour work day. 8

9. Activity Durations Solution: Part 1 Duration (units of time) = Quantity / Production per unit of time x number of crews = 1400 / 175 x 1 = 8 days Cost (labor cost) = Duration x crew cost per unit of time = 8 days x 1800 / day = 14400 PKR Total direct cost =14400 + 4.5 units of material x 1000 / day x 8 days = 50400 PKR Part 2 Unit cost = total cost / quantity = 50400 / 1400 = 36 PKR/ unit 9

10. Activity Durations Sometimes the productivity of a specific crew is expressed in man-hours/unit not units/day. For example, if the productivity is said to be 0.5 Man-hour/cubic meters, this means how long it will take one labor to construct one unit. This way, it can be applied to any crew formation and work hours. 10

11. Activity Durations Example: What is the duration in days to install 600 square feet of walls shuttering if: Crew of 2 carpenters is used with output of 200 square feet/day Productivity is measured as 0.008 man-hour/square feet. Number of carpenters =3, and number of working hours/day = 8 hours 11

12. Activity Durations Solution: Part A Duration = 600 / 200 = 3 days Part B Total man-hours needed = 600 x 0.008 = 48 man-hours (if one man used) Duration = 48 / 8 = 6 days (if one man used) Duration using 3 men = 6 / 3 = 2 days 12

13. Activity Durations Example: The construction of a reinforced concrete wall involves placing 660 m 3 concrete, fixing 50 ton of steel, and 790 m 2 of formwork. The following information belongs to the jobs involved in this activity: A 6 man concrete crew can place 16 m 3 of concrete/day. A steel-fixer and assistant can fix 0.5 ton of reinforcement/day. A carpenter and assistant can fix and remove 16 m 2 of shuttering/day. Calculate the duration of the activity considering the steel-fixer as the critical resource. 13

14. Activity Durations Solution: Using one steel-fixer: duration = 50 / 0.5 = 100 days Using one carpenter: duration = 790 / 16 = 49.4 days Using one concreting crew: duration = 660 / 16 = 41.25 days. Then, for a balanced mix of resources, use 2 steel-fixer crews, one carpenter crew, and one concreting crew. Accordingly, the activity duration = 50 / 0.5 x 2 = 50 days. 14

15. Activity Durations Example: Consider the activity “Drive piles, abutment #1”. The pile‐driving production rate is 70 linear feet per hour. Each abutment involves the driving of twenty‐eight 40‐foot‐long piles. 15

16. Activity Durations Solution: 28 piles×40 ft /pile = 1,140 ft 1,140 ft ÷70 ft / hr = 16.3 hrs 16

17. Activity Durations An estimated activity duration is the time required for its usual accomplishment and does not include any allowance for random or unusual happenings. (Deterministic durations) An estimated completion time for the entire project can be computed by using such estimates of individual activity times. The actual project completion time probably will vary from this estimated value for various reasons that cannot be entirely predicted or quantified. The time estimates are made based on the assumption that “normal” conditions will prevail. 17 Time Contingency Deterministic Durations are used in CPM

18. Activity Durations There are many possibilities of “abnormal” occurrences that can substantially increase the actual construction time. Concessions for abnormal or random delays are accounted for in a number of ways, the simplest being a contingency allowance. Where these occurrences can be recognized as activity specific, the contingency may be added in the form of an uncertainty variance to the activity duration. (Random Durations) 18 Time Contingency Random Durations are used in PERT

19. Thanks 19